The number of rentstabilized units over time has been steadily declining. In 2008, there were ~892,700, and in 2021, there were ~802,500. These data come from SOA tax bills eg:


Residential housing project completions and permits, over time by type of permit owner. Project completions have generally decreased for individual permit holders the last few years, while corporation held permits have been increasing. The permit data, which will be predictive of project completions in the future, shows a large increasing gap between individuals and corporations, with permits held by corporations increasing at a fast rate. These data come from
NYC DCP housing database


Residential project permits by owner, 2022